1. Field of the Invention
This invention relates to apparatus and methods used in specialized, minimally invasive surgery, and more particularly to techniques for minimizing the amount of fluid absorbed within a patient during surgeries utilizing irrigation flows.
2. Description of Related Art
Laparoscopic techniques for performing certain surgical procedures have been widely adopted because they often simplify a given operation, reduce the trauma to the patient, and shorten recovery time. In procedures such as hysteroscopy and prostatectomies using trans-urethral resection, the operative site must be constantly irrigated as the surgeon views the site through an endoscope while manipulating the laparoscopic instruments. Irrigation is essential not only to visualization, but also to transporting surgical debris, blood and tissue, away from the site. However, as pointed out in U.S. Pat. No. 5,492,537 to Vancaillie (xe2x80x9cthe ""537 patentxe2x80x9d), there are problems associated with such procedures. Because some of the fluid will be absorbed in the body instead of being transported away, there is a danger of pulmonary edema or electrolytic imbalance if too much fluid is absorbed. Consequently, the ""537 patent discloses a fluid monitoring system which determines, on an ongoing basis, the amount of fluid absorbed by measuring the mass of fluid supplied from a source and the mass of fluid collected from the operative site. If indications are that too much fluid is being absorbed, measures can be taken.
The system of the ""537 patent operates by using gravity to feed irrigation fluid from an elevated source to a fluid source channel in the probe used by the surgeon to observe the operative site. Concurrently, irrigation fluid is collected from the operative site via a fluid collection channel in the probe, while overflow from the operative site proceeds outwardly through the body orifice into a fitted drape system feeding a funnel-like drain bag. The fluid from the collection channel and drain bag is drawn into collection canisters by a common negative pressure source for disposal or examination. By monitoring the weight of the source fluid delivered and waste fluid collected, the system can calculate an approximate value for fluid absorbed.
A high irrigation flow rate is needed to insure full lavage and adequate visibility at the operative site. To minimize absorption of fluid within the patient and the passage of fluid from intravascular to interstitial spaces, outflow of fluid through the probe""s collection channel (and therefore the negative pressure or suction level in the channel) must be substantial and continuous. In practice, however, this result is not readily achieved. Where the suction force in the probe collection channel and the drain bag are produced by the same negative pressure source, as in the ""537 patent, suction forces generated by the negative pressure source are often powerful enough to keep the drain bag empty. As a result, the open drain line and empty drain bag can draw large quantities of air, taxing the suction capabilities of the negative pressure source and reducing the suction force in the probe collection channel and at the probe tip. Consequently, suction at the operative site can be partially lost, resulting in both excessive fluid absorption in the body and diversion of excess fluid into the drain bag.
Systems and methods in accordance with the invention employ a bifurcated tubing system joined at a junction that leads to a single line feeding into a suction canister system that creates an imbalance within a predetermined range between the suction drawn at the scope collection channel and the suction available at the drain bag. To create this imbalance, the flow path in the branch of the bifurcated system between the junction and the drain bag is of substantially higher flow impedance than the conduit to the scope collection channel. Suction forces acting on the irrigation fluid withdrawn from the operative site are thus substantially higher in the scope collection channel, and therefore the scope collection channel transports the majority of fluid away from the operative site. This in turn assures superior clarity and easier visualization within the operative site, and reduces the amount of overflow from the body orifice (vagina or urethra). Consequently, gravity flow into the drain bag is reduced, and even though the flow is restricted, the suction acting at the bottom of the drain bag is adequate to empty fluid collected in the drain bag. The higher flow impedance can be established at a selected level by a reduced diameter section, a tubing of smaller inner diameter or a resiliently deformable member responsive to pressure, each being configured to provide the proper balance of flows given overall flow impedances, but designed to be compatible with a low cost disposable system.
Methods in accordance with the invention combine separate outflows of irrigation fluid from a body cavity, the flow paths each being arranged to exert suction from a common source in a different manner. The suction in a principal flow path through a probe in the cavity and a port in an endoscope or other device is kept substantially constant at a level which withdraws the majority of the irrigation fluid, thus minimizing absorption of fluid within the patient and enabling improved observation through the endoscope. It also reduces overflow from the body cavity, some of which is inevitable, into a fitted drape on the patient, and then into a drain bag, under gravity forces. Suction on the bottom of the drain bag is exerted from the common source, but the flow rate is limited, which insures that suction on the principal line is not reduced.